This is the black sickle-wielding ninja. Once he is brought down to half health, he teleports away, and pulls out an extra sickle to do more damage.
He is meant to be more of a mid-level enemy, around level 15-ish, but it can be scaled to be easier or harder. I'm kind of leaving it to you to pick the damage and health, unless you want me to. In that case, feel free to comment me.